Wyo. Stat. Ann. § 35-11-1432

Except tanks within operating facilities, any underground or aboveground storage tank that has been temporarily out of use for more than twelve (12) months shall be permanently closed in accordance with department rule and regulation not later than twelve (12) months after the date on which the tank is placed in temporarily out of use status or July 1, 2018, whichever is later, unless a time extension is authorized in writing by the department.